It is known that upon a flight, the violent turbulence related to vertical wind gusts, can cause at the aircraft:                large vertical acceleration variations which, when negative, are likely to injure aircraft passengers;        a large deviation of the aircraft in altitude, which increases the collision risk with another aircraft;        lift peaks on the airfoil, which test the maximum load rating thereof; and        roll moments, as well as lateral accelerations, which are also likely to injure aircraft passengers.        
Two atmospheric turbulence types are generally responsible for the troubles caused to an aircraft, that is:                clear air turbulence events, of the CAT (“Clear Air Turbulence”) type, which represent wind shears which often occur without being perceptibly visible, generally above 15,000 feet (about 4,500 meters). Such clear air turbulence events which are of the non-convective type, most often occur near the tropopause, rather above the mountains and rather in winter. These turbulence events represent a natural risk upon a flight and can bring about injuries for the passengers under some particularly harsh conditions. Moreover, such turbulence events bring about a further fuel consumption (for avoiding the turbulence area) and contribute to the fatigue of the aircraft and pilots; and        convective turbulence events which often are visible through clouds being present. The harsh convective turbulence events occur in rather humid regions, such that a radar can generally detect them. Thus, most of the time, this phenomenon can be avoided by aircrafts. However, pilots may be surprised or may not have time to bypass an area of convective turbulence events. The harshest turbulence events occur in storm clouds, with current ascents and downdroughts that can reach several tens of meters per second. These convective turbulence events are quite localised and less expanded than clear air turbulence events.        
Often, the previous phenomena which are localised surprise both the aircraft crew and the piloting systems on board, that do not have time to carry out the operations suitable for attenuating effects thereof, in particular the side ones, which occur at the aircraft level.
From patent applications FR-0510341 and WO-2007/042652, it is known a device for attenuating on an aircraft the effects of a vertical turbulence event undergone by this aircraft upon a flight.
The object of the present invention is to attenuate exclusively the side effects generated by a turbulence event. However, it is not limited to the above-mentioned atmospheric turbulence events, but can also relate to wake turbulence events which, by definition, are likely to occur in an aircraft wake, accordingly at any altitude. Indeed, the cause of such wake turbulence events is not due to atmospheric phenomena, but to the presence of an aircraft ahead the aircraft undergoing the turbulence event.
On the other hand, it is known:                from U.S. Pat. No. 3,007,656 an automatic pilot which is used to stabilise an aircraft with respect to its primary axes, in particular upon a turbulence event. This prior document provides accelerometers for measuring accelerations along each of these axes and means for calculating roll, pitch and yaw control commands intended to compensate for such accelerations, these control commands being applied to that end to usual control surfaces of the aircraft; and        from U.S. Pat. No. 6,095,459, a system for counteracting asymmetrical aerodynamic forces that may be generated on a multiengine aircraft, in particular in case of an engine breakdown of said aircraft. To this end, this prior document provides means for counteracting an undesirable yaw and roll, by maintaining a zero sideslip angle.        